A few lessons learned.
The cheap egg shaped rubber pump/check valve the came with the cheap vacuum pump system leaked. I replaced it with a brake bleeding brass vacuum hand pump with a gauge (from HF). The vacuum gauge which will indicate leaks and amount of vacuum necessary to achieve a full erection.
The thin seal that came with the vacuum pump cylinder had several immediate problems. The inter-seal on the penis shaft was painfully tight and the seal on the outside of the cylinder leaked. I had to use rubber bands around the outside of the seal to stop the leak. The thin seal provided very little if any padding on the pubic bone.
I found a thick clear gel seal that works on both a 2" & a 3" diameter cylinders. Outside diameter of the seal is ~3.25" & the outside wall is ~3/8" thick gel (the gel is very strong & does stretch.) The clear gel seal padding between the end of the plastic vacuum cylinder and pubic area is also 3/8" thick gel (about 6 times thicker than the original seal). I cut a beveled edge on the thick padded seal opening into vacuum tube. The penis opening is ~1.5" diameter. Hope this description makes sense.
My purpose for the vacuum pump was to flood the cavernous tissue daily to insure penis tissue was fully stretched and prevent atrophy & loss of erect penis length
Measurement mod. Turn the vacuum tube (with seal), opening down on a hard surface such a countertop. Pump a vacuum to your normal level. Using a ruler measure upward from the countertop/seal and mark each inch on a piece of tape. Also mark your personal maximum length or goal. Then use sharp metal tool or "d r e me l" tool to permanently mark each inch (or mm if you are metric) and your maximum length on the plastic tube. (penis length in mm sounds bigger than in inches
)First time! Take your time! If you never used a penis vacuum pump system before, do not initially pump a lot of vacuum. What is a lot of vacuum? It occurs when a testicle or two get sucked under the seal, through a hole already occupied by a penis and into the vacuum tube . It can happen very quickly and will water your eyes. For a quick release valve, I drilled a 1/4" hole in the side of the tube and cover it with a small piece of duct tape. Fold one edge of the tape so that you can grab it hurry.
Regarding pubic hair: I keep it trimmed short which reduces sealing problems and reduces the chance hair getting pulled or caught.